1. Field of the Invention
The present invention relates to a liquid cooling structure of an electric motor such as an induction motor, and more particularly, to a jacket for cooling a stator and a method of manufacturing the same and an improvement in the structure of a liquid cooled motor using the jacket.
2. Description of the Related Art
For the purpose of enhancing the cooling efficiency in an electric motor and relieving the peripheral equipment from being adversely affected by heat dissipation, there has been proposed a liquid cooled motor which includes a casing 1 having liquid cooling conduits 2, which serves as a cooling jacket for a stator 3, as shown in FIGS. 3 (PRIOR ART) and 4 (PRIOR ART).
In this case, the casing 1 is usually sand-cast from aluminum alloy, and housings 4 and 5 are separately attached to the front and rear surfaces, respectively, of the casing 1 by ordinary bolts. This entails the following problems.
Due to characteristics of the casting, the wall portions of the casing 1, inevitably involve cavities 7 in the interior or on the surface thereof, which may cause liquid leakage if the casing 1 is used as the liquid cooling structure. In particular, the cavities 7 are liable to be exposed on the inner surface or the end surface which has been subjected to cutting operations, thereby causing the leak of the coolant. In order to fill the cavities 7, there may be needed, for example, a time-consuming and costly treatment requiring casing 1 to be dipped into the special sealing compound after being cast.
It is also impossible to provide the sand-casting with deep holes and threaded holes having an accurate configuration by the sand-casting process alone. Hence, if they are needed, the sand-casting must be subjected to further cutting operation after casting. In addition, due to the impossibility of obtaining a higher dimensional accuracy, a fine or complicated sectional configuration is unable to be provided on the interior of the liquid cooling conduits 2.
Further, at least eight ordinary bolts 6 must be used to fasten the front and rear housings to the casing 1, involving a large number of assembling steps which not only may cause an unevenness in the screw torque of the bolts 6 but also requires a greater precaution to ensure a uniform fastening.